Method for the preparation of sulfonic acid esters from free sulfonic acids

ABSTRACT

Sulfonic acids, particularly amido-substituted sulfonic acids and preferably acrylamidoalkanesulfonic acids, can be esterified by reaction with (A) an ester of phosphoric acid or (B) an adduct of an ester of a strong acid (preferably sulfuric acid) with an amide such as dimethylformamide. This method is especially useful for the preparation of lower alkyl esters, especially the methyl and ethyl esters. The esters are useful monomers, especially for copolymerization with acrylic compounds to produce polymers of improved dyeability.

This invention relates to new methods for preparing compositions ofmatter, and particularly for preparing sulfonic acid esters. Still moreparticularly, it relates to a method for the preparation of a sulfonicacid ester which comprises reacting the corresponding sulfonic acid witha compound having one of the formulas ##EQU1## AND ##EQU2## wherein:

R¹ is a monovalent aliphatic, cycloaliphatic or arylaliphatic radical ora corresponding substituted radical;

EACH OF R² and R³ is hydrogen or a hydrocarbon or substitutedhydrocarbon radical;

Z⁻ is an anion; and

Y IS 1, 2 OR 3.

The preparation of sulfonic acid esters, especially the alkyl esters,cannot ordinarily be effected by convenient means from the free sulfonicacid. The most usual method for the preparation of these compounds is toconvert the acid to the sulfonyl chloride and to react said sulfonylchloride with an alcohol. This method is cumbersome since it involvestwo steps, and somewhat hazardous since the reagents used to convert theacid to its chloride are toxic and difficult to handle. Likewise, directesterification reagents such as diazomethane are not entirely safe.

A principal object of this invention, therefore, is to provide a newmethod for the preparation of sulfonic acid esters.

A further object is to provide a convenient one-step method forpreparing esters of sulfonic acids in high yield.

Still another object is to provide a method for sulfonic acid esterpreparation which does not involve the use of dangerous reagents.

A further object is to prepare esters of unsaturated sulfonic acids, andparticularly acrylamidoalkanesulfonic acids.

Other objects will in part be obvious and will in part appearhereinafter.

Any sulfonic acid may be esterified by the method of this invention.Thus, suitable acids include aliphatic ones such as methanesulfonicacid, ethanesulfonic acid, 2-propanesulfonic acid and the like; aromaticacids such as benzenesulfonic acid, p-toluenesulfonic acid,2-naphthalenesulfonic acid and the like; heterocyclic sulfonic acidssuch as 3-pyridinesulfonic acid; amido-substituted sulfonic acids suchas 2-acetamidopropanesulfonic acid, 2-acrylamidopropanesulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, 4-acrylamidobenzenesulfonicacid and the like. The particularly preferred acids, for the purpose ofthis invention, are those containing aliphatic olefinic bonds andespecially simple olefinic sulfonic acids and acrylamidoalkanesulfonicacids, such as 2-methyl-2-propenesulfonic acid and2-acryl-amido-2-methylpropanesulfonic acid.

As previously indicated, the method of this invention involves the useof an esterification reagent having one of two structures, hereinaftersometimes referred to as reagent A and reagent B. Reagent A is analiphatic, cycloaliphatic or arylaliphatic ester of phosphoric acid andmay be a monoester, diester, triester or mixture of two or more of suchesters, but the triesters (those in which y is 3) are preferred. In suchphosphoric acid esters, R¹ may be aliphatic, cycloaliphatic orarylaliphatic or a substituted derivative of any of these. By"substituted" is meant radicals containing substituents which do notalter significantly their character or reactivity. Examples are:

Halide (fluoride, chloride, bromide, iodide)

Hydroxy

Ether (especially lower alkoxy wherein "lower" denotes radicalscontaining up to seven carbon atoms)

Keto

Carboxy

Ester (especially lower carbalkoxy)

Aminoacyl (amide)

Nitro

Cyano

Thioether

Sulfoxy

Sulfone

Sulfonic acid (and derivatives thereof)

In general, no more than three such substituent groups will be presentfor each 10 carbon atoms in the radical.

In the preferred compounds used as reagent A, R¹ will be a lower alkylradical, especially methyl or ethyl.

Reagent B which may also be used in the method of this invention is aquaternary imidate which may be prepared by the reaction of a suitableamide with an ester of a strong acid. In reagent B, R¹ is as previouslydefined. Each of R² and R³ is hydrogen or a hydrocarbon or substitutedhydrocarbon radical; the term "hydrocarbon radical" as used hereinincludes aliphatic, cycloaliphatic and aromatic (including aliphatic-and cycloaliphatic-substituted aromatic and aromatic-substitutedaliphatic and cycloaliphatic) radicals.

The following are illustrative of hydrocarbon radicals within the scopeof this invention. Where a named radical has several isomeric forms(e.g., butyl), all such forms are included.

    ______________________________________                                        Methyl            Benzyl                                                      Ethyl             Cyclohexyl                                                  Propyl            Cyclopentyl                                                 Butyl             Methylcyclopentyl                                           Hexyl             Cyclopentadienyl                                            Octyl             Vinylphenyl                                                 Decyl             Isopropenylphenyl                                           Vinyl             Cinnamyl                                                    Allyl             Naphthyl                                                    Ethynyl                                                                       Propargyl                                                                     Phenyl                                                                        Tolyl                                                                         Xylyl                                                                         ______________________________________                                         ##EQU3##

Many obvious variations of these radicals will be apparent to thoseskilled in the art and are included within the scope of the invention.

Substituted hydrocarbon, alkyl, aryl, etc., radicals (the word"substituted" being defined hereinabove) are considered fully equivalentto the hydrocarbon, alkyl, aryl, etc., radicals and to be part of thisinvention.

Preferably, the hydrocarbon or substituted hydrocarbon radicals inreagent B are free from ethylenic and acetylenic unsaturation and haveno more than about 30 carbon atoms, desirably no more than about 12carbon atoms. A particular preference is expressed for compounds inwhich R² is hydrogen and R³ is a lower alkyl radical, the word "lower"being defined hereinabove. Still more preferably, R³ is methyl.

The anion Z⁻ is derived from the strong acid ester previously mentioned.Thus, when the ester is a dialkyl sulfate Z⁻ is the monoalkyl sulfateanion.

A reagent particularly useful as reagent B can be prepared by thereaction of dimethyl sulfate with dimethylformamide in approximatelyequimolar amounts, as described in the examples hereinafter. Thisreaction is known in the art and is described, for example, in GermanPatent No. 1,156,779.

The reaction between the sulfonic acid (or a salt thereof which isfrequently equivalent to the free acid for the purposes of thisinvention) and reagent A or B is most conveniently effected at atemperature of about 50°-200°C., preferably about 70°-150°C. In general,a somewhat higher temperature is employed with reagent A than withreagent B. The reaction may be carried out in a suitable diluent such asacetone, ethylene glycol monomethyl ether, benzene, toluene,dimethylformamide, dimethyl sulfoxide or the like. The proportions ofreagents used are not critical, although it is preferred to use at leastone mole of reagent A or B per mole of sulfonic acid in order to convertas much sulfonic acid as possible to the desired ester. Generally, anexcess of reagent A or B (typically about a twofold to fourfold excess)is used.

Following the completion of the esterification reaction, the desiredester may be recovered and purified by typical methods known in the art.

The method of this invention is illustrated by the following examples.All parts are by weight unless otherwise indicated.

EXAMPLE 1

A mixture of 41.4 parts (0.2 mole) of2-acrylamido-2-methylpropanesulfonic acid, 73 parts (0.4 mole) oftriethyl phosphate and 0.2 part of p-methoxyphenol (a polymerization andoxidation inhibitor) is heated to 120°-135°C. for 1-3/4 hours, withstirring. After 40 minutes, the slurry becomes homogeneous. Unreactedtriethyl phosphate is removed under vacuum at 90°C., and during theremoval 0.1 part of "Irganox 1010" (another inhibitor) is added. Theresidue is washed twice with hexane and dissolved in benzene; thebenzene solution is washed with a saturated sodium sulfate solution,dried over magnesium sulfate and evaporated. The solid product isrecrystallized from a benzene-hexane mixture. The hexane washings arediluted with methylene chloride and the solution is used to extract theaqueous sodium sulfate washings, dried over magnesium sulfate andevaporated. The combined crystalline product is the desired ethyl2-acrylamido-2-methylpropanesulfonate and melts at 65°-67°C. The yieldis 28.1 parts, or 60% of theoretical.

EXAMPLE 2

Following a procedure similar to that of Example 1, ethyl2-methyl-2-propenesulfonate is prepared by the reaction of2-methyl-2-propenesulfonic acid with triethyl phosphate.

EXAMPLE 3

A mixture of 63 grams (0.5 mole) of dimethyl sulfate and 37 grams (0.5mole) of dimethylformamide is heated at 60°-80°C. for 3 hours. There arethen added 52 grams (0.25 mole) of 2-acrylamido-2-methylpropanesulfonicacid, 700 ml. of benzene and 0.3 gram each of p-methoxyphenol,t-butylcatechol and 2,6-di-t-butylcresol. The mixture is heated underreflux, with stirring, for 24 hours and then most of the benzene isremoved by distillation. Refluxing at 78°-80°C. is continued for 24hours, after which the mixture is cooled and poured into 300 grams ofice water, and an additional 300 ml. of benzene is added. The organicand aqueous phases are separated and the aqueous phase is extracted withchloroform. The combined organic layers are dried over magnesium sulfateand the solvents are stripped. The desired methyl2-acrylamido-2-methylpropanesulfonate is recrystallized from toluene;after recrystallization, it melts at 77°-80°C.

EXAMPLE 4

An addition product of dimethyl sulfate and dimethylformamide isprepared according to the method of Example 3. To 0.5 mole of thisproduct is added a mixture of 59 grams (0.25 mole) of sodium2-acrylamido-2-methylpropanesulfonate, 0.1 gram of p-methoxyphenol and500 ml. of benzene. The mixture is heated under reflux, with stirring,for three hours, after which the benzene is evaporated under vacuum. Theremaining solid is recrystallized from a benzene-cyclohexane mixture toyield the desired methyl 2-acrylamido-2-methylpropanesulfonate.

EXAMPLE 5

Following a procedure similar to that of Example 4,methyl-p-toluenesulfonate is prepared by the reaction of 0.5 mole ofp-toluenesulfonic acid with one mole of the dimethylsulfate-dimethylformamide reaction product.

Sulfonic acid esters, as a class, may be used as latent sources of thecorresponding sulfonic acids (e.g., by reaction with an alcohol) and asalkylating agents.

Esters of polymerizable sulfonic acids, such as methyl2-methyl-2-propenesulfonate and methyl2-acrylamido-2-methylpropanesulfonate, may be polymerized underfree-radical conditions, either alone or in the presence of othermonomers. The term "polymer", as used herein, includes additionhomopolymers, copolymers, terpolymers and other interpolymers.

Polymerization by the free-radical method may be effected in bulk,solution, suspension or emulsion, by contacting the monomer or monomerswith a polymerization initiator either in the absence or presence of adiluent at a temperature of about 0°-200°C. Suitable initiators includebenzoyl peroxide, tertiary butyl hydroperoxide, acetyl peroxide,hydrogen peroxide, azobisisobutyronitrile, persulfate-bisulfite,persulfate-sodium formaldehyde sulfoxylate, chlorate-sulfite and thelike.

A large variety of polymerizable compounds can be used to forminterpolymers with sulfonic acid esters. They include (1) unsaturatedmonohydric alcohols and esters thereof, (2) unsaturated acids and estersthereof, (3) unsaturated polyhydric alcohols and esters thereof, (4)vinyl cyclic compounds, (5) unsaturated ethers, (6) unsaturated ketones,(7) unsaturated amides, (8) unsaturated aliphatic hydrocarbons, (9)unsaturated alkyl halides, (10) unsaturated acid anhydrides, (11)unsaturated acid chlorides, and (12) unsaturated nitriles. Specificillustrations of such compounds are:

1. Unsaturated alcohols and esters thereof: Allyl, methallyl, crotyl,1-chloroallyl, 2-chloroallyl, cinnamyl, vinyl, methylvinyl, 1-phenallyl,butenyl alcohols, and esters of such alcohols with saturated acids suchas acetic, propionic, butyric, valeric, caproic and stearic; withunsaturated acids such as acrylic, alpha-substituted acrylic (includingalkylacrylic, e.g., methacrylic, ethylacrylic, propylacrylic, etc., andarylacrylic such as phenylacrylic), crotonic, oleic, linoleic andlinolenic; with polybasic acids such as oxalic, malonic, succinic,glutaric, adipic, pimelic, suberic, azelaic and sebacic; withunsaturated polybasic acids such as maleic, fumaric, citraconic,mesaconic, itaconic, methylenemalonic, acetylenedicarboxylic andaconitic; and with aromatic acids, e.g., benzoic, phenylacetic,phthalic, terephthalic and benzoylphthalic acids.

2. Unsaturated acids (examples of which appear above) and esters thereofwith saturated alcohols, such as methyl, ethyl, propyl, isopropyl,butyl, isobutyl, sec-butyl, tert-butyl, 2-ethylhexyl, cyclohexyl orbehenyl alcohols.

3. Unsaturated polyhydric alcohols, e.g., butenediol, and esters thereofwith saturated and unsaturated aliphatic and aromatic, monobasic andpolybasic acids, examples of which appear above.

4. Vinyl cyclic compounds including styrene, o-, m-, p-chlorostyrenes,bromostyrenes, fluorostyrenes, methylstyrenes, ethylstyrenes andcyanostyrenes; di-, tri-, and tetra-chlorostyrenes, bromostyrenes,fluorostyrenes, methylstyrenes, ethylstyrenes, cyanostyrenes;vinylnaphthalene, vinylcyclohexane, divinylbenzene, trivinylbenzene,allylbenzene, and heterocycles such as vinylfuran, vinylpyridine,vinylbenzofuran, N-vinylcarbazole, N-vinylpyrrolidone andN-vinyloxazolidone.

5. Unsaturated ethers such as methyl vinyl ether, ethyl vinyl ether,cyclohexyl vinyl ether, octyl vinyl ether, diallyl ether, ethylmethallyl ether and allyl ethyl ether.

6. Unsaturated ketones, e.g., methyl vinyl ketone and ethyl vinylketone.

7. Unsaturated amides, such as acrylamide, methacrylamide,N-methylacrylamide, N-phenylacrylamide, N- allylacrylamide,N-methylolacrylamide, N-allylcaprolactam, diacetone acrylamide andhydroxymethylated diacetone acrylamide.

8. Unsaturated aliphatic hydrocarbons, for instance, ethylene,propylene, butenes, butadiene, isoprene, 2-chlorobutadiene andalpha-olefins in general.

9. Unsaturated alkyl halides, e.g., vinyl fluoride, vinyl chloride,vinyl bromide, vinylidene chloride, vinylidene bromide, allyl chlorideand allyl bromide.

10. Unsaturated acid anhydrides, e.g., maleic, citraconic, itaconic,cis-4-cyclohexene-1,2-dicarboxylic andbicyclo(2,2,1)-5-heptene-2,3-dicarboxylic anhydrides.

11. Unsaturated acid halides such as cinnamoyl, acrylyl, methacrylyl,crotonyl, oleyl and fumaryl chlorides or bromides.

12. Unsaturated nitriles, e.g., acrylonitrile, methacrylonitrile andother substituted acrylonitriles.

The especially preferred polymers are the copolymers with acrylicmonomers; that is, with acids such as acrylic and methacrylic acids andtheir esters, amides and nitriles. Copolymers with acrylonitrile areespecially useful for the preparation of textile fibers because of theiraffinity for dyes.

The preparation of polymers of polymerizable sulfonic acid esters isillustrated by the following examples.

EXAMPLE 6

A resin flask is charged with 100 ml. of a 0.0008 N sulfuric acidsolution, flushed with nitrogen and heated to 50°C. There are then addedsimultaneously, with stirring, the following: (1) a mixture of 100 gramsof acrylonitrile and 3.4 grams of methyl2-acrylamido-2-methylpropanesulfonate, (2) a solution of 0.75 part ofpotassium persulfate in 100 ml. of water, (3) a solution of 2.1 parts ofsodium metabisulfite in 100 ml. of water, and (4) 100 ml. of a 0.0024 Nsolution of sulfuric acid. The addition time for the four solutions is55 minutes. After addition is complete, the flask is cooled in ice waterand the contents are poured into 3 liters of water. The desiredcopolymer precipitates and is washed with water and dried in a vacuumoven at 70°C. It is found to have excellent incorporation of Sevron Blue2G dye.

EXAMPLE 7

Following substantially the procedure of Example 6, a copolymer isprepared from 100 parts of acrylonitrile and 3.4 parts of methyl2-methyl-2-propenesulfonate.

EXAMPLE 8

A mixture of 47.5 parts of styrene, 2.5 parts of methyl2-acrylamido-2-methylpropanesulfonate and 0.1 part ofazobisisobutyronitrile is heated overnight at 100°C., under nitrogen.During this time, the mixture solidifies. It is dissolved in benzene andreprecipitated by pouring into methanol. The precipitate is thenfiltered, washed with methanol and dried; it is the desired copolymer.

EXAMPLE 9

A mixture of 209.9 parts of isodecyl acrylate, 11.05 parts of methyl2-acrylamido-2-methylpropanesulfonate and 331 parts of heptane is heatedto 60°C. under nitrogen, with stirring. Azobisisobutyronitrile, 0.44part, is then added and stirring is continued at 60°C. for 20 hours,yielding a heptane solution of the desired copolymer.

What is claimed is:
 1. A method for the preparation of a sulfonic acidester containing the moiety -SO₃ R¹ which comprises reacting thecorresponding sulfonic acid or a salt thereof with a compound having theformula R¹ O-CH=N⁺(R³)₂ R¹ SO₄ ⁻, wherein each of R¹ and R³ is a loweralkyl radical.
 2. A method according to claim 1 wherein R³ is methyl. 3.A method according to claim 2 wherein the sulfonic acid contains analiphatic olefinic bond.
 4. A method according to claim 3 wherein thesulfonic acid is an acrylamidoalkanesulfonic acid.
 5. A method accordingto claim 4 wherein the acrylamidoalkanesulfonic acid is2-acrylamido-2-methyl-propanesulfonic acid.
 6. A method according toclaim 5 wherein R¹ is methyl or ethyl.